Coolant recovery system

ABSTRACT

A system and process for recovering high purity coolant gas from at least one fiber optic heat exchanger, characterized by controlling a flow of coolant gas into and out of the heat exchanger using a pressure, impurity and/or flow rate monitoring or transmitting means in conjunction with a flow adjusting or controlling device to limit air or other gas infiltration into at least one fiber optic passageway of the heat exchanger. A sealing means may also be used at at least one end of the fiber optic passageway to further reduce air or other gas infiltration into the passageway. The resulting high purity coolant gas from the outlet of the heat exchanger is delivered to the inlet of the heat exchanger. Optionally, the resulting coolant gas from the outlet of the heat exchanger may be cooled, filtered and/or purified before being delivered to the inlet of the heat exchanger.

This application is a Continuation of prior U.S. application Ser. No.07/989,392, filing date Dec. 11, 1992, now U.S. Pat. No 5,377,491,issued Jan. 3, 1995.

FIELD OF THE INVENTION

The present invention relates in general to coolant gas recoverysystems, more particularly to helium recovery systems associated withoptical fiber cooling means.

BACKGROUND OF THE INVENTION

In the production of optical fibers, a glass rod or preform, which isespecially made to manufacture optical fibers, is processed in anoptical fiber drawing system. The optical fiber drawing system generallycomprises a furnace, a heat exchanger, a coating applicator, a dryer orcuring furnace and a spool as shown by European Patent Application No.0,079,188. Initially, the glass rod or preform is melted in the furnaceto produce a small semi-liquid fiber. The semi-liquid fiber is thencooled and solidified as it falls through the air and through the heatexchanger. The cooled and solidified fiber from the heat exchanger iscoated in the coating applicator, dried in the curing furnace or dryerand drawn with the spool.

The drawing rate of the optical fiber is dependent on the cooling rateof the optical fiber in the heat exchanger. That is, the rate at whichthe fiber can be withdrawn can be increased as the rate of coolingincreases. To increase the rate of cooling, a coolant gas, such ashelium or nitrogen, is normally introduced into the heat exchanger todirectly cool the semi-liquid fiber by direct heat exchange. The directheat exchange is made possible by designing the heat exchanger toprovide a passageway or cylindrical hole running from the top to thebottom for passing the optical fiber, an inlet for introducing thecoolant into the passageway or cylindrical hole and optionally at leastone outlet for removing the coolant from the passageway or cylindricalhole. The flow of the coolant into the heat exchanger is usuallycontrolled with metering valves and flow meters.

Although the drawing rate of the optical fiber is increased throughemploying the above heat exchanger, the coolant utilized is normallylost to the atmosphere through one or both ends of the passageway orcylindrical hole and/or the outlet, and is also contaminated withimpurities, e.g., when air impurities infiltrate into the passageway orcylindrical hole where the coolant is located. Replacing this lostcoolant gas represents a substantial cost to the optical fibermanufacturing process. Thus, there is a need for an effective andefficient coolant recovery system and heat exchanger, which could reducethe coolant losses and reduce the contamination of the coolant.

SUMMARY OF THE INVENTION

The present invention is in part drawn to a recovery system which isuseful for recovering coolant gas efficiently and effectively. Therecovery system comprises:

(a) at least one heat exchanger having at least one passageway capableof passing at least one hot fiber, at least one inlet for passingcoolant gas into said at least one passageway and at least one outletfor recovering coolant gas from said at least one passageway;

(b) means for pumping coolant gas from said outlet of the said at leastone heat exchanger to said inlet of said at least one heat exchanger;

(c) means for monitoring and/or transmitting the flow rate of a coolantgas from the outlet of said at least one heat exchanger, theconcentration of impurities in a coolant gas from the outlet of said atleast one heat exchanger and/or the pressure of a coolant gas from theoutlet of at least one heat exchanger; and

(d) means for controlling the flow of a coolant gas into and out of saidat least one heat exchanger based on the monitored and/or transmittedvalue to limit air or other gas infiltration into said at least onepassageway of said at least one heat exchanger.

At least one volume for damping surges in coolant gas flow may beprovided prior to the means for pumping a coolant gas to better controlthe pressure and/or flow of a coolant gas delivered to the means forpumping. The coolant gas derived from the means for pumping may becooled with cooling means, may be filtered with filtering means and/ormay be purified in a purification system before it enters the inlet ofat least one heat exchanger. At least one of the cooling means employedmay be incorporated into at least one heat exchanger.

The present invention is also drawn to a heat exchanger system which isuseful for improving the recovery of coolant gas in the above coolantrecovery system. The heat exchanger system comprises:

(a) at least one passageway capable of passing therethrough at least onehot fiber, said at least one passageway having at least two endopenings;

(b) at least one inlet for introducing coolant gas into said at leastone passageway:

(c) at least one outlet for recovering coolant gas from said at leastone passageway; and

(d) means for monitoring and/or transmitting the flow rate of a coolantgas from the outlet of said at least one heat exchanger, theconcentration of impurities in a coolant gas from the outlet of said atleast one heat exchanger and/or the pressure of a coolant gas from theoutlet of at least one heat exchanger; and

(e) means for controlling the flow of a coolant gas into and out of saidat least one heat exchanger based on the monitored and/or transmittedvalue to limit air or other gas infiltration into said at least onepassageway of said at least one heat exchanger.

In the vicinity of at least one of the end openings of the passageway,sealing means may be placed. The sealing means is designed to minimizeor reduce the infiltration or egress of gases into or out of thepassageway but allow the passage of at least one hot fiber. The sealingmeans may be selected from the group consisting of labyrinth seals, gasseals, mechanical seals, tolerance seals and/or liquid seals. In lieu ofthe sealing means, a furnace for melting a glass rod or preform and acoating applicator may be sealed onto the top and bottom of the heatexchanger, respectively, to minimize air infiltration and enhance therecovery of coolant gas.

As used herein the term "at least one hot fiber" means one or more ofany fiber which needs to be cooled.

As used herein the term "in the vicinity of" means a surrounding area ofa designated point or location. Typically, it covers an area between thecoolant gas outlet and the closest end opening in the heat exchangerand/or between the coolant gas inlet and the closest end opening in theheat exchanger.

As used herein the term "coolant gas" means any gas capable of coolinghot optical fibers.

As used herein the term "mechanical seal" means any mechanical devicethat seals the end openings of a passageway or provides sealing means inthe vicinity of the end openings of the passageway by direct contactwith at least one fiber passing through the passageway.

As used herein the term "tolerance seals" means any feature that can beused to reduce the end openings of a passageway or reduce the passagewayin the vicinity of the end openings with minimum or no contact with atleast one fiber which goes through the passageway.

As used here the term "gas impurities" means any gas other than acoolant gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a coolant recovery system which isone embodiment of the present invention.

FIG. 2 shows a heat exchanger and a recovery conduit having at least onemonitoring and/or transmitting means and at least one controlling means,which are one embodiment of the present invention.

FIG. 3 shows a heat exchanger having labyrinth seals, which is oneembodiment of the present invention.

FIG. 4 shows a furnace and coating applicator which are attached to thetop and bottom of the heat exchanger.

As shown by the above figures, there are several preferred embodimentswhich are useful for recovering the coolant gas with the reducedcontamination. These preferred embodiments, however, in no way precludeother embodiments which will become apparent to those skilled in the artafter reading this disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is illustrated a schematic diagram of acoolant gas recovery system. The coolant gas recovery system comprises,among other things, a plurality of heat exchangers (1(a) to 1(f)), atleast one collector vessel (3), at least one compressor (5), at leastone cooling means (7), at least one filtering means (9), at least onepurification system (11), at least one product vessel (13) and at leastone coolant storage tank (15). The coolant recovery system may becoupled to any conventional optical fiber drawing system which utilizesat least one of the heat exchangers (1(a)-1(f)).

As shown by FIGS. 2-4, at least one of the heat exchangers (1(a)-1(f))has at least one passageway (100) capable of passing therethrough afiber, at least one inlet (101) for introducing a coolant gas into thepassageway (100) and at least one outlet (102(a) and/or 102(b)) forrecovering or removing the coolant gas from the passageway (100). Thepassageway (100), which normally runs through the top to the bottom ofthe heat exchanger to cause the end openings to be present at the topand the bottom, may have expanded cross-sectional areas at certainlocations (103(a)-103(c)) along its length. The expanded cross-sectionalarea may directly communicate with the inlet (101) and outlet (102(a)and/or 102(b)) so that a large volume of a coolant gas can be recoveredor introduced into the passageway (100). These expanded areas(103(a)-103(c)) may be located at the mid section of the passageway(100) and/or in the vicinity of the end openings of the passageway(100). Depending on the location, the coolant gas can be fed into thepassageway (100) in a desired manner, e.g., countercurrently withrespect to the direction of a fiber, since the coolant is fed to orrecovered from these areas.

In the vicinity of the end openings of the passageway (100), preferablybetween the end openings and the outlet (102(a) or 102(b)) closest tothe end openings, at least one sealing means (104) may be located. Thesealing means (104) minimizes or reduces the infiltration and/or egressof gases into and/or out of the passageway (100) through the endopenings and, at the same time, provides an opening or openingssufficient to pass a fiber through the passageway (100). The preferredsealing means may be selected from labyrinth seals, gas seals,mechanical seals, tolerance seals and/or liquid seals. Of thesepreferred sealing means, a labyrinth seal may be useful because itincreases the pressure drop in the gas flow path between the endopenings and the outlet closest to the end openings by a series ofexpansions (108) and contractions (109). In certain circumstances, afluid seal may be advantageously utilized. To use a fluid seal, such asair, nitrogen or carbon dioxide, however, at least one additional inlet(105), which is in fluid communication with the passageway (100), may beneeded. The flow of the fluid seal may be controlled with a flow meter(111) and a valve (112). As used herein the term "fluid seal" meansadding a fluid into the passageway at a point between the coolant gasinlet and the closest end opening of the passageway and/or between thecoolant gas outlet and the closest end opening of the passageway toalter a flow distribution and/or pressures inside of the passageway toincrease the recovery of the coolant gas and/or decrease theinfiltration of contaminants.

It is understood that the heat exchanger can be designed to providefeatures which are functionally equivalent to the sealing means orfeatures which can accommodate a combination of the above sealing means.For example, a furnace (106) for melting a glass rod or preform and acoating applicator (107) for coating a fiber may be sealed onto the topand bottom of the heat exchanger, respectively, with or without asealing means (110) since the heat exchanger is commonly used betweenthe furnace (106) and the coating applicator (107) in the conventionaloptical fiber drawing systems. To this arrangement, additional sealingmeans, such as a gas seal, may also be used to further reduce air orother gas infiltration into the passageway.

Initially, the coolant gas is introduced into a plurality of the heatexchangers at about 0 to about 150 psig. The coolant gas, albeit can bederived from any source, is derived from the storage tank (15). From thestorage tank (15), the coolant gas flows through, among other things, abranch conduit (16) and a plurality of coolant feed conduits(17(a)-17(f)) which are in fluid communication with the inlets of theheat exchangers. The coolant feed conduits have metering valves(18(a)-18(f)) and flow meters (19(a)-19(f)), which are useful forcontrolling the flow of the coolant gas into the heat exchanger. Thecoolant gas employed may be at least one of helium, nitrogen, hydrogen,carbon dioxides, etc. Of these coolant gases, a gas containing at leastabout 80% by volume helium is normally preferred.

As the coolant gas enters the heat exchangers, i.e., passageways, itflows toward the outlets of the passageways. The outlets of thepassageways are connected to recovery conduits (20(a)-20(f)). At leastone of the recovery conduits has means (22(a)-22(f)) for monitoringand/or transmitting the flow rate of a coolant gas from the outlet ofsaid at least one heat exchanger, the concentration of impurities in acoolant gas from the outlet of said at least one heat exchanger and/orthe pressure of a coolant gas from the outlet of at least one heatexchanger and means (21(a)-21(f)) for controlling the flow of a coolantgas into and out of said at least one heat exchanger based on themonitored and/or transmitted value to limit air or other gasinfiltration into said at least one passageway of said at least one heatexchanger. The means for monitoring and/or transmitting may be selectedfrom flow meters, pressure sensors, impurity or gas analyzers (oxygenanalyzer) and/or any known means while the means for controlling may beat least one flow resistance means, such as valves, orifices, sinteredfilters, narrow pipes having smaller diameters than the recovery conduitor packed beds. The adjustment of the flow resistance means can be mademanually or automatically based on the flow rate, pressure and/orcomposition of a coolant gas in each recovery conduit. Alternatively,the flow resistance means can be preset or preadjusted based onexperience and calculation or based on the flow rate, pressure and/orcomposition of a coolant gas in each recovery conduit. In operation, thecomposition of a coolant gas may be determined by ascertaining theconcentration of oxygen in the coolant gas with an oxygen analyzer. Onthe other hand, a coolant gas flow rate and pressure may be determinedby using a flow meter and a pressure sensor, respectively. By adjustingthe flow resistance means, such as metering valves, to control thepressure in the vicinity of the outlets, i.e., locations in thepassageway, which directly communicates with the outlets, the improvedrecovery of the coolant gas may be obtained without substantialcontamination. Generally, greater than about 50% of the coolant gas canbe recovered using this arrangement. Any remaining coolant is normallyallowed to flow out of the end openings of the passageways to limit airor other fluid contamination, or air or other gas infiltration into thepassageways. Of course, if the sealing means or equivalents thereof isused in conjunction with this arrangement, the recovery of the coolantgas can be further improved since a smaller amount of the coolant gas isneeded to prevent or reduce air or other fluid contamination. Thelabyrinth seal, for example, increases the pressure drop in the gas flowpath between the end openings and the outlet closest to the end openingsby creating or providing a series of expansions and contraction. If theair or other fluid contamination cannot be eliminated, one or some ofthe solenoid or other valves (23 (a)-23(f)) may be used to isolate thehighly contaminated coolant gas from particular heat exchangers, or apurification system (11) may be used to remove one or more fluidcontaminants. Also, the purification system can be used to allow higherlevels of the coolant gas recovery by removing contaminants that mayflow into the heat exchanger during the higher coolant gas flow orhigher coolant recovery rate.

The recovered coolant gas in the recovery conduits is allowed to flowinto a volume for dampening surges in a coolant gas flow, which may be arecovery branch conduit (24) or an optional gas collection vessel (3).If the recovery branch conduit (24) is used as the volume for dampeningsurges in the coolant gas flow, its length and internal diameter, whichare dependent on the volume of the coolant gas from the recoveryconduits, should be properly sized to damp surges in the coolant gasflow. The use of the optional gas collection vessel (3), however, isnormally preferred because it may also be useful for reducing pressurefluctuations and enhancing coolant gas flow control.

From the recovery conduit (24) and/or from the gas collection vessel(3), the coolant gas flows to means for pumping the coolant gas (5),such as a recovery compressor, through a conduit (25) having a valve(26). The means for pumping the coolant gas compresses the coolant gasfrom a slight vacuum (typically about 5 to about 14.6 psia) to apressure sufficient for recirculation (typically about 5 to 250 psig).The compressed coolant gas flows into optional cooling means (7) througha conduit (27). In the cooling means, the compressed coolant gas iscooled. After cooling, oil, water and/or particulate may be removed fromthe coolant gas via optional filtering means (9).

At least a portion of the compressed coolant gas which may have been ormay not have been cooled and/or filtered may be automatically recycledto the means for pumping the coolant gas through a recycle conduit (28)having a valve (29), or through the recycle conduit (28) having thevalve (29) and a portion of the conduit (25). The recycle conduit isuseful for controlling the pressure in the volume for dampening surgesin the coolant gas flow, e.g., the gas collector vessel, and forcontrolling the flow rate of the coolant gas. At least one means(30(a)-30(c)) for monitoring the pressure condition of the volume, theflow rate of the coolant gas derived from the volume and/or the puritylevel of the coolant gas in the volume may be utilized to adjust thevalve(s) (26 and/or 29) or other equivalent flow resistance means (notshown) in order to control the flow rate of the coolant and the pressurein the volume, e.g., the vessel (25). A means for transmitting themonitored value may be installed in the means (30(a)-30(c)) so that thevalves (26 and/or 29) or other equivalent flow resistance means can beautomatically adjusted with control means (31) and/or (32) based on themonitored and/or transmitted conditions to control the pressure in thevolume, e.g., the vessel (25) and the flow rate of the coolant gas fromthe volume, e.g., the vessel (25). The control may be done manually orautomatically using electronic, pneumatic or hydraulic signals.

The remaining portion of the compressed coolant gas may be sent to theoptional purification system (11) through a conduit (42) having a valve(43). The optional purification system may be selected from, inter alia,filtration systems, solid and fluid separation systems, cryogenic liquidupgrading systems, chemical adsorption systems, catalytic reactionsystems, absorption systems, membrane separation systems and/or pressureand/or thermal swing adsorption systems. Of these systems, the membraneseparation systems and pressure and/or thermal swing adsorption systemsare preferred because the purified coolant gas, such as helium, need notbe highly pure in cooling at least one hot fiber. Of course, cryogenicgas separation systems can be also useful because the purified coolantgas need not be further cooled. These systems may be or may not be usedwith a dryer depending on the moisture level of the coolant gas enteringthe purification system.

In the desired membrane purification system, the purification of thecompressed coolant gas may be carried out as indicated below. Initially,the compressed coolant gas may be fed to at least one membrane module toproduce a waste stream and a product stream. The non-permeated streammay be used as the waste stream while the permeated stream is used asthe product stream. The recovered product stream is delivered to aplurality of the heat exchangers directly or through optional productvessel (13) and the branch conduit (16). An optional compressor (notshown) may be used to deliver the product stream to the heat exchangers.If necessary, at least a portion of the product stream can be recycledback to the means for pumping the coolant gas through a conduit (33) tocontrol the pressure in the volume, e.g., the vessel (3). In themeantime, the waste stream may be treated with additional membranemodules to produce second product streams. The second product streamsmay be recycled to the means for pumping the coolant gas through aconduit (34) if their purity levels are sufficiently high. If not, theymay be treated with other purification means, such as an optional dryer,before they are sent to the means for pumping the coolant gas, or theymay be discarded through a conduit (35). Additional membrane stages maybe used to increase the recovery of the coolant gas and/or the purity ofthe coolant gas.

The compressed coolant gas, which may have been or may not have beencooled, filtered and/or purified, is delivered to the product vessel(13). The product vessel may be useful for reducing pressurefluctuations and/or improving the control of a coolant gas flow rate. Tothis product vessel, a makeup coolant gas may be delivered from thestorage tank (15) through a conduit (36) having valves (37 and 38) tocombine with the compressed coolant gas to makeup for any lost coolantgas. The combined stream is delivered to the heat exchangers through aconduit (16) having a valve (39). The stream may be cooled withadditional cooling means (not shown) before it is introduce into theheat exchangers and/or may be cooled with additional cooling means (notshown) which may have been incorporated or integrated into the heatexchangers. The integrated cooling means may be one or more additionalpassageways or reservoirs in the heat exchangers. By filling thesepassageways or reservoirs of the heat exchangers with liquid nitrogen,liquid helium, liquid argon and like, the coolant gas in the passagewaysfor passing at least one fiber can be cooled by indirect heat exchange.

When the concentration of impurities, e.g., the concentration of oxygen,in the recovered coolant gas from the heat exchanger exceeds theallowable limit (typically about 1 mole % to about 50 mole %), themakeup coolant gas is directly delivered to the heat exchangers througha conduit (40) having a valve (41). Meanwhile, the recovery systemassociated with recovering the coolant gas from the outlets of the heatexchangers can be isolated or shut down to reduce or prevent thecontamination of the coolant gas. Of course, the coolant gas can alwaysbe directly delivered to the heat exchangers if the recovery system isshut down for any other reasons.

Although the coolant recovery system of the present invention has beendescribed in detail with reference to certain embodiments, those skilledin the art will recognize that there are other embodiments of theinvention within the spirit and scope of the claims.

What is claimed is:
 1. A coolant recovery system comprising:(a) at leastone heat exchanger having at least one passageway capable of passingtherethrough at least one hot fiber, at least one inlet for passingcoolant gas in and to said at least one passageway and at least oneoutlet for removing coolant gas from said at least one passageway; (b)means for pumping coolant gas from said outlet of the said at least oneheat exchanger to said inlet of said at least one heat exchanger; (c)means for monitoring or transmitting at least one process conditionselected from the group consisting of a flow rate of coolant gas fromthe outlet of said at least one heat exchanger, a concentration ofimpurities in coolant gas from the outlet of said at least one heatexchanger and pressure of coolant gas from the outlet of at least oneheat exchanger; and (d) means for controlling a flow of coolant gas intoand out of said at least one heat exchanger based on a monitored ortransmitted value to limit air or other gas infiltration into said atleast one passageway of said at lease one heat exchanger.
 2. The coolantrecovery system according to claim 1, further comprising means forcooling coolant gas prior to its entrance into said inlet of said atleast one heat exchanger.
 3. The coolant recovery system according toclaim 1, further comprising at least one volume for damping surges incoolant gas flow.
 4. The coolant recovery system according to claim 3,wherein said means for monitoring is at least one pressure sensor, atleast one flow meter or at least one impurity or gas analyzer at atleast one recovery conduit which is in direct communication with theoutlet of said at least one heat exchanger.
 5. The coolant recoverysystem according to claim 1, wherein said mains for controlling a flowof coolant gas in and out of said at least one heat exchanger is atleast one coolant gas flow resistance means.
 6. The coolant recoverysystem according to claim 5, wherein said at least one gas flowresistance means is at least one valve and flow meter located at said atleast one recovery conduit useful for controlling a pressure conditionor flow at the outlet of said at least one heat exchanger.
 7. Thecoolant recovery system according to claim 6, further comprising atleast one metering valve and at least one flow meter, which are used tocontrol a flow of coolant gas into said at least one heat exchanger. 8.The coolant recovery system according to claim 7, further comprisingsealing means located in at least one end of said at least onepassageway of said heat exchanger to reduce or minimize air infiltrationinto said at least one passageway and, at the same time, provide anopening or openings capable of passing a fiber therethrough.
 9. Thecoolant recovery system according to claim 8, wherein said sealing meansis labyrinth seals which are located in both end openings of said atleast one passageway of said heat exchanger.
 10. The coolant recoverysystem according to claim 8, wherein said sealing means comprises afurnace and a coating applicator, which are sealed to the top and bottomof said heat exchanger, respectively, so that air infiltration into saidat least one passageway of said heat exchanger is reduced or minimized.11. The coolant recovery system according to claim 1, further comprisingfiltering means for removing at least one impurity selected from thegroup consisting of oil, water and particulate from the coolant gasderived from said outlet of said heat exchanger.
 12. The coolantrecovery system according to claim 1, further comprising a purificationsystem for removing fluid contaminants from the coolant gas and derivedfrom said means for pumping.
 13. The coolant recovery system accordingto claim 12, wherein said purification system is a membrane separationsystem, a pressure swing adsorption system, a thermal swing adsorptionsystem or cryogenic gas separation system.
 14. The coolant recoverysystem according to claim 1, further comprising a product vessel forcombining makeup coolant and coolant gas derived from said means forpumping.
 15. The coolant recovery system according to claim 1, whereinsaid system contains coolant gas.
 16. The coolant recovery systemaccording to claim 15, wherein said coolant gas contains at least about80% by volume of helium.
 17. A coolant recovery system comprising:(a) atleast one heat exchanger having at least one passageway capable ofpassing hot fibers, at least one inlet for passing coolant gas into saidat least one passageway and at least one outlet for removing coolant gasfrom said at least one passageway; (b) at least one volume for dampingsurges in coolant gas flow in communication with said outlet of said atleast one heat exchanger; (c) means for pumping coolant gas from saidoutlet of the said at least one volume to said inlet of said at leastone heat exchanger; (d) means for monitoring or transmitting at leastone condition selected from the group consisting of a pressure conditionof coolant gas in said at least one volume, a flow rate of coolant gasderived from said at least one volume and a purity level of coolant gasderived from said at least one volume; and (e) means for controlling aflow of coolant gas directed to said means for pumping coolant gas basedon a monitored or transmitted condition.
 18. A heat exchanger systemcomprising:(a) at least one passageway capable of passing through atleast one hot fiber, said at least one passageway having at least twoend openings; (b) at least one inlet for introducing coolant gas intosaid at least one passageway; (c) at least one outlet for recoveringcoolant gas from said at least one passageway; and (d) means formonitoring or transmitting at least one condition selected from thegroup consisting of a flow rate of coolant gas from the outlet of saidat least one heat exchanger a concentration of impurities in coolant gasfrom the outlet of said at least one heat exchanger and pressure ofcoolant gas from the outlet of at least one heat exchanger; and (e)means for controlling a flow of a coolant gas into and out of said atleast one heat exchanger based on a monitored or transmitted value tolimit air or other gas infiltration into said at least one passageway ofsaid at least one heat exchanger.
 19. The heat exchanger systemaccording to claim 18, further comprising sealing means in the vicinityof said at least two openings of said at least one passageway, or afurnace for melting a glass rod and a coating applicator for coatingoptical fiber, which seal said at least two openings of said at leastone passageway.